[binutils-gdb] Clean up testsuite compiler_info support.

[sergiodj+buildbot at redhat dot com]

*** TEST RESULTS FOR COMMIT a97b16b8fcfc7ac818c43c9f9457966cfc47aed6 ***

Author: Doug Evans <dje@google.com>
Branch: master
Commit: a97b16b8fcfc7ac818c43c9f9457966cfc47aed6

Clean up testsuite compiler_info support.
gdb/testsuite/ChangeLog:

	* gdb.base/watchpoint.exp (test_complex_watchpoint): Remove
	compiler_info references.
	* gdb.cp/temargs.exp: Ditto.
	* lib/gdb.exp: Unset compiler_info instead of setting to "unknown".
	(get_compiler_info): Early exit if already computed.  Set compiler_info
	to "unknown" if there was a problem.
	(test_compiler_info): Add function comment.  Call get_compiler_info.